Several types of sensors have a primary axis along which the sensor is most sensitive. When using such sensors, it is often desirable to orient the sensor with its primary axis directed in a particular direction. For example, if acceleration of an object in a particular direction is to be sensed, the primary axis of an accelerometer used to sense the acceleration of that object preferably should be oriented in the direction in which the object accelerates. Another example is where multiple sensors are used to sense a phenomenon (such as acceleration) in three dimensions. Three sensors can be oriented so that the primary axes of the sensors are orthogonal to one another. In other words, the primary axis of a first sensor can be directed along an X-axis, the primary axis of a second sensor can be directed along a Y-axis, and the primary axis of a third sensor can be directed along a Z-axis. Thus, the three sensors can be used to sense in three dimensions.
Difficulties can arise, however, when sensors (such as integrated circuit sensors) are mounted on printed wiring boards (PWBs) or other generally planar substrates. Several types of conventional sensors that are designed to be mounted on PWBs are typically designed either with the primary axis directed perpendicular to the major plane of the PWB (referred to herein as perpendicular axis sensors) or with the primary axis directed parallel to the major plane of the PWB (referred to herein as parallel axis sensors). If a particular application calls for the primary axis of the sensor to be oriented in a direction other than the direction provided by mounting the sensor directly to the PWB (for example, parallel to the major plane of the PWB for a perpendicular axis sensor or perpendicular to the major plane of the PWB for a parallel axis sensor), the sensor cannot be directly mounted to the PWB and have the primary axis directed in the desired direction.
If, for example, three perpendicular axis sensors are used to measure a phenomenon in three dimensions as described above, all three sensors cannot be mounted directly to the PWB and still have the primary axes of the three sensors be orthogonal to each other. In other words, if all three sensors were mounted directly to the PWB, the primary axes of the three sensors would all be oriented in the same direction.
One conventional approach to mounting three sensors to a PWB in order to sense in three dimensions is to attach two, separate smaller PWBs perpendicular to a main PWB at a corner of the main PWB. One sensor is mounted directly to the major surface of the main PWB while the two other sensors are mounted to major surfaces of the two smaller PWBs. In other words, a mounting structure similar to a corner of a box is constructed and one sensor is mounted on each of the three surfaces of the corner mounting structure. Thus, if three perpendicular axis sensors are mounted on each of the three surfaces of the corner mounting structure, the primary axes of the three sensors will be oriented orthogonally with respect to each other.
Such conventional corner mounting structures, however, generally require relatively complex, non-planar electrical interconnect structures that must span the several surfaces of the corner mounting structure in order to connect the sensors mounted on the smaller PWBs to the circuitry on the main PWB. Also, conventional automated PWB assembly techniques and equipment (such as conventional pick-and-place machines) typically cannot be used to, attach the smaller PWBs to the main PWB and to attach the electrical interconnect structure to the corner mounting structure. Therefore, such corner mounting structures often must be hand assembled, which generally increases assembly costs and decreases the total volume of PWBs that can be assembled in a period of time.
Moreover, such corner mounting structures generally increase the overall height of the PWB assembly, which may be undesirable for some applications. Furthermore, corner mounting structures are more prone than standard planar PWBs to deform due to shock and vibration. Also, since the corner mounting structures are often located at a corner of the main PWB, corner mounting structures impose an additional constraint on the layout of the other PWB components.
Another conventional approach to mounting three sensors to a PWB in order to sense in three dimensions is to include three sensors in a single, three-dimesional sensor module. For example, in the tri-axial accelerometer, Model No. 2420, commercially available from Silicon Designs, Inc. of Issaquah, Wash., three accelerometers are mounted within a single case. The accelerometers are arranged within the case so that the primary axes of the accelerometers are orthogonal with respect to each other. However, such sensor modules tend to be relatively thick and, as a result, tend to increase the overall height of the assembled PWB. Also, such a configuration is not optimal for all applications, and not all sensors are available in such multi-sensor modules.